[iOS] Added Upgrading docs for 2.6.0 to 2.7.0
Upgrading projects is fun. Added update scrupt instructions.
[CB-3320] minor doc syntax fix in camera.getPicture.md
Fixed code example poor formatting in FileTransfer docs
[CB-3022] add default textbox value for notification.prompt

- document adding default textbox value parameter for notification.prompt
[CB-2598] remove iOS doc reference to navigator.fileMgr API

-remove iOS doc reference to non-existing navigator.fileMgr API
[CB-3043] Fix broken images on all Windows guides.
[CB-3043] Fix broken links in all Windows guides.